This invention relates generally to the field of fuel storage and pumping systems. More specifically, the present invention relates to the field of valves and fittings used in such systems, and particularly to the class of devices known as shear fittings.
Fuel storage and delivery systems for service stations and the like are constructed in a variety of configurations. Typically, fuel is stored in a large underground tank for delivery, via an above-ground pump, to motor vehicles. Such systems are generally divided into two categories: submersible systems and suction systems. In both types of systems, the fuel is conducted from the tank to the pump through a fuel pipe that enters the pump below the ground. In suction systems, a negative (subatmospheric) pressure is applied at the pump end of the fuel pipe to dispense the fuel. A check valve is installed in the fuel pipe at or near its juncture with the pump, that is, at the pump inlet. The check valve opens in response to the application of the subatmospheric pressure to its downstream side by the pump, and closes in response to pump shut-off, thereby maintaining "prime" in the pipe.
It has become standard practice to incorporate a peripheral "shear groove" in the external wall of the check valve housing on the upstream side of the valve seat. The shear groove provides a weakened, frangible wall portion that will break if the pump is accidentally knocked over. By providing such a break point near the pump inlet, damage to buried fuel piping is minimized. If the valve is broken at the shear groove, there will be a loss of "prime" in the pipe below the valve, causing the fuel to fall back into the tank. Fuel that is in the pipe above the shear groove is prevented from spilling by the check valve element, because, as previously mentioned, the shear groove is upstream from the valve seat.
One drawback to the incorporation of the shear groove in the check valve housing itself is that the entire check valve assembly must be replaced in the event of a break. Not only is such replacement relatively expensive, but it presents a potential for the leakage of fuel captured between the check valve and the pump.
Another drawback stems from recent legislation that requires verification that an angle check valve or a foot valve is not present in the system. The prior art check valves offer no convenient means for such verification without removal of the entire valve assembly.
There has been, therefore, a long-felt need for means for providing the shear groove function, without requiring the removal of the entire valve assembly in the event of a shear groove break, thereby minimizing leakage of fuel between the shear groove and the pump. There has been a further need for providing, along with such shear groove means, some convenient means for verifying the absence of an angle check valve or a foot valve in the system, without removal of the check valve assembly.